Children with brain tumors are generally followed by imaging studies, such as MRI. Difficulty arises in trying to distinguish tumor regrowth from treatment-related edema, necrosis or radiation injury. Proton nuclear magnetic resonance (1H-MRSI) imaging is a noninvasive method of detecting and measuring cellular metabolites in vivo. 1H-MRSI complements MRI by giving chemical information in conjunction with spatial information obtained by MRI. This study is being conducted to determine 1H-MRSI imaging patterns before, during and after chemotherapy in pediatric patients with brain tumors in an effort to identify and characterize specific patterns of metabolites related to tumor regrowth, response to therapy, edema or necrosis. Using maximum CHO:NAA ratios, we have been able to classify patients with recurrent CNS tumors who have a particularly poor prognosis. e.g. patients with a CHO:NAA>4.0 typically die within 1 year. We are continuing to follow survivors long-term to determine if changes in CHO:NAA will be predictive of tumor recurrence or response.